Polyimides that are obtained by condensation polymerization of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether have superior heat resistance and electrical insulating capacity and are used primarily for flexible printed circuit boards. Most recently, their uses have been expanded to semiconductor packages. High processability and capacity for high precision are required, a high modulus of elasticity, low thermal expansion characteristics like that of metals and low water absorbing capacity are sought as the characteristics of polyimides and various studies have been conducted. For example, in Japanese Patent Application Public Disclosure No. 60-210629 [1985], Japanese Patent Application Public Disclosure No. 64-16832 [1989], Japanese Patent Application Public Disclosure No. 64-16833 [1989], Japanese Patent Application Public Disclosure No. 64-16834 [1989], Japanese Patent Application Public Disclosure No. 1-131241 [1989] and Japanese Patent Application Public Disclosure No. 1- 131242 [1989], an example of a three component polyimide comprised of pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and p-phenylenediamine is described in which p-phenylenediamine is used in combination as the diamine component for the purpose of increasing the modulus of elasticity. Expansion to a four component polyimide can also be effected by adding 3,3'-4,4'-biphenyltetra-carboxylic acid dianhydride to the aforementioned three-component system for the purpose increasing the modulus of elasticity. Examples of four component polyimides are described in Japanese Patent Application Public Disclosure No. 59-164328 [1984] and Japanese Patent Application Public Disclosure No. 61-111359 [1986]. In addition, an attempt to improve the physical properties of four component polyimides by controlling the procedure of addition of the monomers during polymerization is presented, for example, in Japanese Patent Application Public Disclosure No. 5-25273 [1993]. Further, an attempt to improve physical properties by drawing during film making is described, for example, in Japanese Patent Application Public Disclosure No. 1-20238 [1989].
A high modulus of elasticity, low thermal expansion capacity equivalent to that of metals and low water absorbing capacity are necessary as characteristics for use in semiconductor packages as described above. Although the three-component polyimides that are obtained in Japanese Patent Application Public Disclosure No. 60-210629 [1985], Japanese Patent Application Public Disclosure No. 64-16832 [1989], Japanese Patent Application Public Disclosure No. 64-16833 [1989], Japanese Patent Application Public Disclosure No. 64-16834 [1989], Japanese Patent Application Public Disclosure No. 1-131241 [1989] and Japanese Patent Application Public Disclosure No. 1-131242 [1989] have a higher modulus of elasticity than the polyimides that are obtained from pyromellitic dianhydride and 4,4'-diaminodiphenyl ether, a modulus of elasticity sufficient for use as semiconductor packages cannot be obtained. Further, with the four-component polyimides that are obtained in Japanese Patent Application Public Disclosure No. 59-164328 [1984] and Japanese Patent Application Public Disclosure No. 61-111359 [1986], it is necessary to use a large quantity of p-phenylenediamine for the purpose of obtaining a sufficient modulus of elasticity. As a result, there is the problem that the coefficient of thermal expansion becomes excessively lower than that of the metal. With the four component polyimide described in Japanese Patent Application Public Disclosure No. 5-25273 [1993], the modulus of elasticity and thermal expansion capacity are sufficient for this use. However, there is the problem that there is a high coefficient of water absorption. Further, with the three-component polyimide that is obtained in Japanese Patent Application Public Disclosure No. 1-20238 [1989], there are the problems in that the modulus of elasticity is markedly increased and that flexibility is lost as a result of drawing, that the coefficient of thermal expansion is considerably decreased and that there are great differences in thermal behavior from the metal when the film is affixed.
Consequently, this invention has the objective of providing a polyimide film of high elasticity, low thermal expansion characteristics equal to those of metal and low water absorbing capacity, a method for its manufacture and metal laminated plates of improved curl in which it is the base material.